Plastic buckets that hold up to ten gallons are used as containers for a large variety of products. Some products such as plaster for covering joints in sheet rock are removed from buckets by removing the entire bucket lid. Other products such as lubricating oils and paint are poured from a small pour spout that is provided in the bucket lid. Generally only one small pour spout is provided in the bucket to reduce the chances of contamination entering the bucket.
Some contents of buckets are removed by a pump. When a pump is used, a suction pipe is inserted into the bucket through the opening for a small pour spout or the bucket lid is removed and replaced by a substitute lid that is part of the pump assembly. Air is allowed to enter the bucket through the small pour spout or through a substitute lid as the contents are removed.
Other contents are removed from buckets by tilting the bucket and pouring the contents out. Frequently the contents, that are being poured from the bucket, create a vacuum inside the bucket. When the vacuum is sufficiently strong, contents will stop pouring from the small pour spout, air will be sucked into the bucket and then the contents resume pouring from the small pour spout. Upon resumption of pouring, the contents initially exit at an increased rate. When pouring something like a lubricating or hydraulic oil into a gear case or sump, the repeated secession and resumption of flow increases the time required to dispense oil. The abrupt changes in flow rate also increase the likelihood of spills. Spills are serious problems if the contents being poured from the bucket are expensive, toxic, corrosive or flammable.